1. Field of Invention
The present invention relates to a semiconductor structure and method for manufacturing the same. More particularly, the present invention relates to a triple well structure and method for manufacturing the same.
2. Description of Related Art
The combining of RF module, mixed signal function block and logic circuit has become a new trend for system on chip (SOC) application in current electronic industry. To avoid the impact of noise to the RF or analog block, triple well structure is usually adopted to isolate from outside devices in P-well or N-well.
A conventional triple well structure is formed on a P-type substrate. A P-type well is located in the P-type substrate under a transistor. A deep N-type well with high energy implant is formed in the P-type substrate under the P-type field. An N-type well ring is formed around the P-type well. The N-type well ring and the deep N-type well together surround the P-type well. The N-type well ring, the P-type well, and the deep N-type well together form a triple well structure. However, the noise signal around −20 db frequency range of interest would still damage the isolation property of a triple well structure.
Therefore, a triple well structure and method for manufacturing the same is required to improve the noise isolation and does not need any additional photolithograph process.